1. A relay is used to:
A. Amplify current
B. Open and close a circuit
C. Convert AC to DC
D. Store electrical energy
Answer: B. Open and close a circuit
2. The basic function of a relay is based on:
A. Electromagnetic induction
B. Semiconductor properties
C. Capacitive coupling
D. Magnetic resonance
Answer: A. Electromagnetic induction
3. Which of the following is NOT a typical component of a relay?
A. Coil
B. Armature
C. Spring
D. Transistor
Answer: D. Transistor
4. In a relay, the coil is energized to:
A. Open the normally closed contacts
B. Close the normally open contacts
C. Both A and B
D. Neither A nor B
Answer: C. Both A and B
5. A normally open relay contact means that the circuit is:
A. Open when the relay is not energized
B. Closed when the relay is not energized
C. Closed all the time
D. Open all the time
Answer: A. Open when the relay is not energized
6. The advantage of using a relay in a circuit is:
A. It reduces the need for mechanical switches
B. It can control high-power devices using low-power signals
C. It amplifies electrical signals
D. It increases the overall resistance of the circuit
Answer: B. It can control high-power devices using low-power signals
7. Which of the following is a typical application of a relay?
A. Protecting electrical circuits from overcurrent
B. Amplifying sound signals
C. Converting AC to DC
D. Regulating voltage in power supplies
Answer: A. Protecting electrical circuits from overcurrent
8. In a relay, the armature is:
A. A fixed part that doesn’t move
B. The part that moves to open or close contacts
C. A component that generates electricity
D. Used to regulate voltage
Answer: B. The part that moves to open or close contacts
9. The coil of a relay is made of:
A. High-resistance material
B. Low-resistance material
C. Magnetic material
D. Insulating material
Answer: B. Low-resistance material
10. The primary purpose of a relay’s contacts is to:
A. Control the current through the coil
B. Transfer energy from the coil to the load circuit
C. Connect the power supply to the relay
D. Protect the relay from damage
Answer: B. Transfer energy from the coil to the load circuit
11. A switch is a device that is used to:
A. Store electrical energy
B. Open or close a circuit
C. Convert AC to DC
D. Increase the voltage in a circuit
Answer: B. Open or close a circuit
12. Which type of switch is commonly used to control lights in a room?
A. Push-button switch
B. Rotary switch
C. Toggle switch
D. Proximity switch
Answer: C. Toggle switch
13. A push-button switch is typically used for:
A. Maintaining a constant current
B. Turning devices on and off momentarily
C. Controlling variable speeds
D. Changing voltage levels
Answer: B. Turning devices on and off momentarily
14. Which of the following is true for a SPDT (Single Pole Double Throw) switch?
A. It has one input terminal and two output terminals
B. It can switch between two different circuits
C. It can control three different circuits at the same time
D. It is the same as a DPDT switch
Answer: B. It can switch between two different circuits
15. A DPST (Double Pole Single Throw) switch has:
A. Two inputs and one output
B. One input and two outputs
C. Two independent switches in one unit
D. Two inputs and two outputs
Answer: D. Two inputs and two outputs
16. Which of the following types of switches is used for controlling large industrial machines?
A. Push-button switch
B. Knife switch
C. Toggle switch
D. Foot switch
Answer: B. Knife switch
17. A reed switch is typically activated by:
A. Heat
B. Light
C. A magnetic field
D. Pressure
Answer: C. A magnetic field
18. A limit switch is used to:
A. Monitor the position of a mechanical part
B. Control the flow of electricity
C. Prevent overvoltage
D. Measure resistance
Answer: A. Monitor the position of a mechanical part
19. A mercury switch operates by:
A. Moving a mercury contact inside a sealed container
B. Detecting changes in resistance
C. Using a magnet to open and close the circuit
D. Using light sensors to activate the switch
Answer: A. Moving a mercury contact inside a sealed container
20. A momentary switch is one that:
A. Can stay in the on or off position
B. Only remains in the on position
C. Does not maintain a constant connection after